Ion beam sample preparation apparatus and methods

ABSTRACT

Disclosed are embodiments of an ion beam sample preparation apparatus and methods for using the embodiments. The apparatus comprises a tilting ion beam irradiating means in a vacuum chamber that may direct ions toward a sample, a shield blocking a portion of the ions directed toward the sample, and a shield retention stage with shield retention means that replaceably and removably holds the shield in a position. The shield has datum features which abut complementary datum features on the shield retention stage when the shield is held in the shield retention stage. The tilting ion beam irradiating means may direct ions at the sample from more than one tilt angle. A rotating shield retention stage is also disclosed which works in concert with the tilting ion beam irradiating means.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior filed non-provisionalapplication Ser. No. 13/082,373 filed Apr. 7, 2011. Non-provisionalutility application Ser. No. 13/082,373 claims the benefit of priorfiled provisional Application No. 61/322,870 filed Apr. 11, 2010.Application Ser. No. 13/082,373 is incorporated herein by reference.Application No. 61/322,870 is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

DESCRIPTION OF ATTACHED APPENDIX

Not Applicable.

BACKGROUND

The present disclosure relates to the use of one or more ion beams toprepare materials for microscopic observation or spectroscopic analysis.Microscopic observational techniques include, but are not limited to,optical microscopy, scanning electron microscopy (SEM), transmissionelectron microscopy (TEM), scanning transmission electron microscopy(STEM), reflection electron microscopy (REM). Spectroscopic analysistechniques include, but are not limited to, x-ray micro-analysis,reflection electron energy-loss spectroscopy (REELS), electronback-scattered diffraction (EBSD), x-ray photoelectron spectroscopy(XPS), and Auger electron spectroscopy (AES). Materials to be viewedunder any microscopic technique may require processing to produce asample suitable for microscopic examination.

Ion beam milling of a material can produce samples that are well suitedfor microscopic examination. An ion beam irradiating device maygenerate, accelerate, and direct a beam of ions toward a sample. Theimpact of ions on the sample sputters material away from the area of ionimpact. Furthermore, the sample surface may be polished by the ion beamto a substantially smooth condition further enhancing observationalproperties of the sample. Regions of interest in the sample may beexposed and polished by the use of ion beams thus making a suitableobservational sample from the material under investigation.

Broad Ion Beam Slope-Cutting (BIBSC), also known as cross sectioncutting using broad ion beam sources or cross section polishing usingbroad ion beam sources, is a rapid method for removing sample materialto expose a smooth and substantially artifact-free cross-sectionalsurface for ultimate analysis by various microscopies andspectroscopies. A notable advantage of the BIBSC technique is high ratesof surface preparation that can exceed tens or hundreds or thousands ofsquare microns per hour, often over sample milling times of tens orhundreds of minutes.

Important considerations to users of the BIBSC technique include:reducing or minimizing the effort and time that the user is occupied inprocessing the sample; reducing or minimizing the number of steps wheredelicate samples are directly handled and at risk for damage, such asduring mounting to sample holders for processing or analysis; reducingor minimizing the time and effort the user is occupied transferring thesample into the ultimate analysis equipment (imaging or spectroscopy),and aligning the coordinates of the prepared sample region to theultimate analysis equipment prior to analysis; ensuring high quality andhigh probability of success in processing and imaging the sample;reducing or minimizing the time that the BIBSC ion milling equipment andsample mounting equipment are occupied for each sample; and ensuringhigh-quality microscopy observation of the sample during sample mountingand ultimate analysis by reducing the working distance required betweenthe sample and the objective or probe-forming lens used for observation.

A sample that has been prepared in the ion beam may be evaluated byvarious methods to determine if the region of interest has beenadequately exposed and prepared for observation. It may happen that theregion of interest in the sample has not been adequately exposed orprepared. Embodiments of the present disclosure address this commonsituation. Embodiments of the present disclosure teach methods andapparatus for repeatably positioning a sample within an ion beam samplepreparation apparatus thereby facilitating accurate processing andreprocessing of a sample. Further embodiments of the present disclosureteach methods and apparatus for preparing the sample using a tilting ionbeam, making use of controlled ion beam tilt angle to expose regions ofinterest in the sample. Further embodiments of the present disclosureteach methods and apparatus for rotating the sample during preparationusing a tilting ion beam, thereby achieving a more consistent and moredesirable surface for later observation.

In consideration of the foregoing points, it is clear that embodimentsof the present disclosure confer numerous advantages and are thereforehighly desirable.

SUMMARY

The present disclosure is directed to ion beam sample preparationapparatus and methods for using the disclosed apparatus to preparesamples for later observation. The apparatus has features to quickly andrepeatably retain and release both unprepared samples and preparedsamples thereby facilitating preparation of samples in the ion beamapparatus and also facilitating the observation of the prepared samplesin an observation apparatus. Features of the disclosure enable accurateand repeatable positioning of the sample both within the ion beam samplepreparation apparatus and also within observation apparatus later usedfor observing prepared samples. Tilting ion beam features of the presentdisclosure allow additional flexibility in exposing regions of interestin the sample. Tilting ion beam features allow the sample to be preparedby the ion beam using more than one tilt angle of the ion beam. Apreviously prepared sample may be replaced in the apparatus and thenprepared using a different tilt angle of the ion beam thereby exposingand preparing a different region of the sample. Further features of thedisclosure teach methods and apparatus for rotating the sample duringpreparation using a tilting ion beam thereby achieving a more consistentand more desirable surface for later observation.

An embodiment according to the present disclosure of an apparatus forion beam sample preparation comprises: an ion beam sample preparationapparatus comprising: a tilting ion beam irradiating means disposed in avacuum chamber and directing an ion beam toward a shield, characterizedin that said tilting ion beam irradiating means projects an ion beamalong a central ion beam axis, the direction of said central ion beamaxis having a tilt angle with respect to said shield; a tilt driveoperably coupled to said tilting ion beam irradiating means andconfigured to move the direction of said central ion beam axis betweenat least two different tilt angles; a shield retention stage disposed inthe vacuum chamber; said shield retention stage comprising: a firstdatum feature; a second datum feature; a shield retention means havingat least a shield releasing position and a shield retaining position;the shield having at least a rigid planar portion, removably andreplaceably held in said shield retention stage, said shield furthercomprising: a proximal sample surface configured to durably adhere thesample to the shield; a first shielding surface disposed in the path ofthe ion beam and positioned to shield a portion of the ion beam directedat the sample when said shield is held in the shield retaining positionof the shield retention means; a third datum feature formed integrallywith said shield, wherein said shield retention means in said shieldretaining position urges said third datum feature to abut said firstdatum feature; and, a fourth datum feature formed integrally with saidshield, wherein said shield retention means in said shield retainingposition urges said fourth datum feature to abut said second datumfeature.

In a related embodiment of the ion beam sample preparation apparatus,the shield retention stage further comprises a fifth datum feature, andthe shield further comprises a sixth datum feature formed integrallywith the shield, wherein the shield retention means in said shieldretaining position urges said sixth datum feature to abut said fifthdatum feature.

In a related embodiment of the ion beam sample preparation apparatus,the first shielding surface meets said proximal sample surface at anangle of less than about 90 degrees and more than about 80 degrees.

In a related embodiment of the ion beam sample preparation apparatus,the first shielding surface meets said proximal sample surface at anangle of less than about 87 degrees and more than about 83 degrees.

In a related embodiment of the ion beam sample preparation apparatus,the first shielding surface is made of non-magnetic material having lowsputtering-yield.

In a related embodiment of the ion beam sample preparation apparatus, atleast a portion of the first shielding surface is made of tantalum ortitanium.

In a related embodiment of the ion beam sample preparation apparatus,the third datum feature is a datum surface, and at least a portion ofsaid datum surface is coextensive with at least a portion of saidproximal sample surface.

In a related embodiment of the ion beam sample preparation, the proximalsample surface has at least one recessed portion configured for theflowing of adhesive between the shield and the sample.

In a related embodiment of the ion beam sample preparation apparatus,the shield further comprises a sample clamping means coupled to theshield and configured to hold the sample against said proximal samplesurface.

In a related embodiment of the ion beam sample preparation apparatus,the shield further comprises: a second shielding surface having aportion disposed in the path of a portion of the ion beam; a shield edgeformed where the first shielding surface meets the proximal samplesurface; and a visible alignment mark on the second shielding surface,configured such that the location of said visible alignment mark is in apredetermined relationship to the region where the ion beam impinges onsaid shield edge when said shield is held in the shield retainingposition of the shield retention means.

In a related embodiment of the ion beam sample preparation apparatus,the shield is made of a cladding material joined to a core material suchthat a portion of the cladding material forms at least a portion of thefirst shielding surface, and a portion of the core material forms thethird and fourth datum features of the shield. In a related embodiment,the cladding material is a non-magnetic material having lowsputtering-yield.

Another embodiment of the present disclosure is directed to an apparatusfor ion beam sample preparation which comprises: a tilting ion beamirradiating means disposed in a vacuum chamber and directing an ion beamtoward a shield, characterized in that said tilting ion beam irradiatingmeans projects an ion beam along a central ion beam axis, the directionof said central ion beam axis having a tilt angle with respect to saidshield; a tilt drive operably coupled to said tilting ion beamirradiating means and configured to move the direction of said centralion beam axis between at least two different tilt angles; a rotatingshield retention stage disposed in the vacuum chamber; said shieldretention stage comprising: a first datum feature; a second datumfeature; a shield retention means having at least a shield releasingposition and a shield retaining position; a rotation axis locatedsubstantially in the plane of the first datum feature; a rotation drivefor rotating the shield retention stage around the rotation axis; theshield having at least a rigid planar portion, removably and replaceablyheld in said shield retention stage, said shield further comprising: athird datum feature formed integrally with the shield, wherein saidshield retention means in said shield retaining position urges saidthird datum feature to abut said first datum feature; a fourth datumfeature formed integrally with the shield, wherein said shield retentionmeans in said shield retaining position urges said fourth datum featureto abut said second datum feature; a first shielding surface disposed inthe path of the ion beam and positioned to shield a portion of the ionbeam directed at the sample when said shield is held in the shieldretaining position of the shield retention means; a proximal samplesurface configured to durably adhere the sample to the shield; a shieldedge formed where the first shielding surface meets the proximal samplesurface, characterized in that said shield edge is held substantiallyperpendicular to said rotation axis when said shield is held in theshield retaining position of the shield retention means.

In a related embodiment of the ion beam sample preparation apparatus,the apparatus is further characterized in that the tilting ion beamirradiating means and tilt drive are adapted to provide at least twodifferent tilt angles in which the central ion beam axis issubstantially perpendicular to said shield edge.

In a related embodiment of the ion beam sample preparation apparatus,the apparatus is further characterized in that the tilting ion beamirradiating means and tilt drive are adapted to provide at least twodifferent tilt angles in which the central ion beam axis substantiallyintersects said rotation axis.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 shows a schematic cross sectional view of an ion beam samplepreparation apparatus according to an embodiment of the presentdisclosure featuring a tilting ion beam irradiating means. The tiltingirradiating ion beam means is shown with the tilting ion beamirradiating means at a first tilt angle.

FIG. 2 shows a schematic cross sectional view of the apparatus of FIG. 1at a second tilt angle.

FIG. 3A shows a perspective view of a shield retention stage retaining ashield with a sample durably adhered to the shield. The figure alsoshows the cross section plane used for FIG. 3B.

FIG. 3B shows a cross-sectional view of the shield retention stage ofFIG. 3A with shield retention means in a shield retaining position.

FIG. 4 shows a cross section similar to that of FIG. 3B, except thatFIG. 4 shows the cross section with the shield retention means in ashield releasing position.

FIG. 5A shows a perspective view of a shield retention stage accordingto the present disclosure, indicating a cross-sectional plane for FIG.5B.

FIG. 5B shows a perspective sectional view of the shield retention stageof FIG. 5A, with the shield positioned in the shield retaining position.

FIG. 6 shows an exploded perspective section view of the shield andshield retention stage of FIG. 5B. Datum features of both the shield andthe shield retention stage are made visible in this view.

FIGS. 7A and 7B show perspective views of a shield according toembodiments of the present disclosure, viewed from the ion beam side ofthe shield.

FIGS. 8A and 8B show perspective views of a shield according toembodiments of the present disclosure, viewed from the proximal sampleside of the shield.

FIG. 9 shows a perspective view of another shield according to thepresent disclosure, viewed from the ion beam side of the shield andhaving a visible alignment feature.

FIG. 10 shows a perspective view of another shield according to thepresent disclosure, viewed from the proximal sample side of the shieldand having a recessed portion to facilitate the flow of adhesive underthe sample.

FIGS. 11A and 11B show perspective views of a shield with a durablyadhered sample, both before (FIG. 11A) and after (FIG. 11B) preparationin an ion beam sample preparation apparatus according to the presentdisclosure.

FIGS. 12A and 12B show an embodiment of a shield with integrated sampleclamping means according to an embodiment of the present disclosure.

FIG. 13A shows a schematic cross sectional view of an ion beam samplepreparation apparatus according to an embodiment of the disclosurefeaturing tilting ion beam irradiating means and a rotating shieldretention stage. The tilting irradiating ion beam means is shown withthe tilting ion beam irradiating means at a first tilt angle.

FIG. 13B shows a schematic cross sectional view of the apparatus of FIG.13A at a second tilt angle.

FIG. 14A shows a schematic perspective view of a rotating shieldretention stage and rotation drive according to embodiments of thepresent disclosure.

FIG. 14B shows a cross-sectional view of the rotating shield retentionstage of FIG. 14A with shield retention means in a shield retainingposition.

FIG. 15A and FIG. 15B show schematic views of embodiments of a shieldcomprising core material and cladding material.

LIST OF REFERENCE NUMBERS APPEARING IN THE FIGURES

-   -   2—ion beam sample preparation thermal management apparatus    -   8—sample    -   10—vacuum chamber    -   18—chamber cover    -   20—ion beam irradiating means    -   22—central ion beam axis    -   36—tilting ion beam irradiating means    -   38—tilt drive    -   40—shield retention stage    -   42—shield retention means    -   42 a—shield retention means first member    -   42 b—shield retention means second member    -   46—shield retaining position    -   48—shield releasing position    -   50—rotating shield retention stage    -   52—rotation drive    -   54—rotation axis    -   56—vacuum seal    -   60—shield    -   61—shielding surface    -   61 a, 61 b, etc.—first shielding surface, second shielding        surface, etc.    -   62—proximal sample surface    -   63—shield edge    -   64—recessed portion    -   65—visible alignment mark    -   66—core material    -   67—cladding material    -   68—sample clamping means    -   70 a, 70 b, 70 c, 70 d, 70 e, 70 f—first datum feature, second        datum feature, third datum feature, fourth datum feature, fifth        datum feature, sixth datum feature.    -   72—datum surface    -   90—vacuum pump means    -   92—pumping manifold

DESCRIPTION

The Broad Ion Beam Slope-Cutting (BIBSC) sample preparation procedurecan be described as a series of process steps, p1-p5:

-   -   p1) Aligning the desired region of the sample to be processed to        a usable portion of an ion shield;    -   p2) Aligning the sample and shield in the BIBSC ion-milling        system such that the desired region of the sample can be        processed by the ion beam or beams;    -   p3) Evacuating the ion-milling system to vacuum levels        appropriate for ion beam milling;    -   p4) Performing the ion-milling operation or operations,        sometimes using a process monitoring step such as in situ        light-microscopy imaging to verify sufficient cut depth and        quality of the cross section;    -   p5) Venting of the BIBSC ion-milling equipment and removal of        the sample from the equipment.

The analysis of prepared BIBSC sample can be described as a series ofprocess steps, p6-p9:

-   -   p6) Introduction of the sample to the ultimate analysis        microscope and initializing the microscope so that analysis can        commence;    -   p7) Finding the location of the prepared cross-sectional surface        by adjusting any number of the microscope's translation stages,        tilt stages, and rotation stages so that the desired area can be        imaged;    -   p8) Performing the desired microscopic or spectroscopic        analyses;    -   p9) Removing the sample from the microscope;    -   p10) After analyzing the sample, a decision may be made to        reprocess the sample to change the cut depth, position, or        angle—traditionally requiring a repeat of p1-p9.

Embodiments of the present disclosure uniquely permit certainefficiencies and capabilities in the processing and subsequentobservation and analysis of BIBSC produced samples. Beneficial features,functions, and aspects of the present disclosure include, but are notlimited to:

-   -   1. Datum features on the shield, shield retention device in the        sample-to-shield mounting apparatus, shield retention device in        the BIBSC ion-mill, shield retention device in the ultimate        analysis equipment allow significant time efficiencies in        processing steps p1, p2 and p7;    -   2. The integral nature of the sample durably adhered to the        shield, and to a lesser extent with the sample merely clamped to        the shield, allows greater certainty in ensuring alignment of        the shield to the sample remains consistent during p4 even over        long time-scales and changes in temperature, whereas quality of        the cross section cutting process is reduced if this precision        alignment is not maintained;    -   3. The integral nature of the sample durably adhered to the        shield in processing step p1 eliminates the requirement for        expensive and sizable fixturing apparatus to maintain their        spatial relationship together throughout the milling operation,        and enables multiple samples to be prepared in advance of        milling without multiple fixturing apparatus;    -   4. The integral nature of the sample durably adhered or clamped        to the shield eliminates the requirement for dismounting the        sample from the shield prior to observation in a microscope,        even in cases where the smallest working distances between        imaging objective and sample are employed. This permits        reduction of both time and risk of damage to the sample during        sample remounting in processing step p6;    -   5. In the case where reprocessing the sample as in step p10 is        performed, the integral nature of the sample durably adhered or        clamped to the shield can eliminate the need for steps p1 and p2        entirely, which significantly reduces processing time and risk        of damage to the sample during sample remounting; and,    -   6. In the case where reprocessing the sample as in step p10 is        performed, the integral nature of the sample durably adhered or        clamped to the shield allows different cross-sectional planes to        be cut very close to the originally cut cross-sectional plane by        varying the angle of ion beam impinging on the sample and        shield.

Turning now to FIG. 1, illustrated is a schematic cross sectional viewof an embodiment of an ion beam sample preparation apparatus 2 accordingto the present disclosure. The embodiment of FIG. 1 is shown comprising:a vacuum chamber 10 in which a sample 8 is prepared; chamber cover 18which seals vacuum chamber 10 from the outside atmosphere; vacuum pumpmeans 90 and pumping manifold 92, which together bring vacuum chamber 10to vacuum levels appropriate for ion beam milling; tilting ion beamirradiating means 36 and tilt drive 38, which creates and directs an ionbeam having a central ion beam axis 22 toward sample 8; a shield 60,which shields at least a portion of sample 8 from at least a portion ofthe ion beam; a shield retention stage 40, which holds and accuratelypositions shield 60 with respect to the direction and extent of the ionbeam; a shield retention means 42, which both retains shield 60 inshield retention stage 40, and also urges shield 60 to remain in aposition whereby the ion beam may prepare sample 8.

With continuing reference to FIG. 1, the ion beam preferably comprisesnoble gas ions. Elements used for the ion beam may include but are notlimited to: Argon, Xenon, and Krypton. The ion beam may also comprise amixture of ions and neutrals. Shield retention stage 40 is disposed invacuum chamber 10 in a predetermined position and orientation withrespect to central ion beam axis 22. Tilting ion beam irradiating means36 and tilt drive 38 enable the ion beam to prepare the sample bydirecting central ion beam axis 22 toward sample 8 from more than onetilt angle with respect to shield 60. FIG. 1 shows tilting ion beamirradiating means 36 operating at a first tilt angle.

FIG. 2 shows the same apparatus as in FIG. 1. However, the apparatus ofFIG. 2 is shown after the tilt drive 38 has operated to move tilting ionbeam irradiating means 36 to a different tilt angle than in FIG. 1.After the sample has been prepared by the ion beam in the vacuumchamber, chamber cover 18 may be opened; then the shield and sample maybe removed for observation in a microscope.

The tilting ion beam irradiating means and drive shown in theembodiments of FIG. 1 and FIG. 2 give the user additional flexibility inpreparing a sample for later observation. In particular, a sample may beprepared at one tilt angle, observed in a microscope, prepared again ata different tilt angle, and observed again. The ability to directcentral beam axis 22 along more than one tilt angle allows forconsiderable refinement in sample preparation in the region of interest.Other aspects of the embodiments shown in FIG. 1 and FIG. 2 may bebetter understood now with reference to the following descriptions andfigures.

FIG. 3A shows a perspective view of shield retention stage 40 on whichsample 8 has been durably adhered to shield 60 prior to placing theshield and sample combination in a shield retaining position 46 inshield retention stage 40. Shield 60 has a shielding surface 61 which ispositioned in relation to sample 8 to shield at least a portion of saidsample 8 from at least a portion of the ion beam. Also shown in FIG. 3Ais a section line indicating the section view shown in FIG. 3B.

FIG. 3B shows a section view illustrating the position and function ofthe shield retention means which is part of shield retention stage 40.FIG. 3B shows an embodiment of the shield retention means comprising ashield retention means first member 42 a and a shield retention meanssecond member 42 b. Shield retention means first member 42 a urgesshield retention means second member 42 b against shield 60. The actionof shield retention means first member also urges shield 60 againstshield retention stage 40, and thereby maintains the position of shield60 within shield retention stage 40 while the sample is prepared by ionbeam. An embodiment of the shield retention means may comprise a springfor shield retention means first member 42 a and a solid member asshield retention means second member 42 b configured to slide within acavity in shield retention stage 40.

FIG. 4 shows a view from the same sectional plane as in FIG. 3B.However, in FIG. 4 the shield and sample have been removed to show ashield releasing position 48 of shield retention means. By means of thetwo positions provided by shield retention means, namely shieldretaining position 46, as shown in FIG. 3A and FIG. 3B, and shieldreleasing position 48, as shown in FIG. 4, a shield may be removably andreplaceably secured in shield retention stage 40. A sample that has beendurably adhered to shield 60 may be processed, removed, and thenreprocessed by simply placing it in the shield retaining position andpreparing the sample again in the ion beam.

FIG. 5A shows a perspective view of shield retention stage 40 on whichshield 60 is retained, wherein said shield has a shielding surface 61.FIG. 5A also shows a sectional plane used for FIG. 5B.

FIG. 5B shows a sectional perspective view illustrating physicalfeatures of both shield 60 and shield retention stage 40 that facilitateaccurate and repeatable positioning of the shield with respect to theshield retention stage. The positioning of shield 60 assures thatshielding surface 61 and shield edge 63 are accurately positioned andaccurately oriented with respect to the shield retention stage, and arepositioned with respect to central ion beam axis 22 to intercept atleast a portion of the ion beam directed toward the sample.

FIG. 6 shows a sectional perspective view as in FIG. 5B, in whichpreferred embodiments of both shield 60 and shield retention stage 40have a plurality of datum features 70 a, 70 b, 70 c, 70 d, 70 e, and 70f. In the exploded view shown in FIG. 6, shield 60 has been removed fromshield retention stage 40 and the shield is turned to expose a proximalsample surface 62, upon which a sample may be durably adhered prior tosample preparation by the ion beam. The plurality of datum features 70a, 70 b, 70 c, 70 d, 70 e, and 70 f is provided on both shield 60 andshield retention stage 40, and they enable accurate and repeatablepositioning of the shield 60 with respect to the shield retention stage40. Datum features 70 b, 70 d, and 70 f on the shield are shaped andpositioned such that when they are caused to abut complementary datumfeatures 70 a, 70 c, and 70 e on the shield retention stage, the shieldmay be held in a predetermined position and a predetermined orientationwith respect to the central ion beam axis 22. Shield retention means 42assures that datum features 70 b, 70 d, and 70 f of shield 60 abut thecorresponding datum features 70 a, 70 c, and 70 e of the shieldretention stage 40 when the shield is held in the shield retainingposition. Shield edge 63, also visible in FIG. 6, is also caused to bein a predetermined position and predetermined orientation when theshield is held in the shield retaining position.

Datum features are arranged in pairs such that a datum feature on theshield has a corresponding datum feature on the shield retention stage.In FIG. 6, one such pair of datum features is datum feature 70 a on theshield retention stage and datum feature 70 b on the shield. Anotherpair of datum features shown in FIG. 6 is datum feature 70 c on theshield retention stage and datum feature 70 d on the shield. Anotherpair of datum features shown in FIG. 6 is datum feature 70 e on theshield retention stage and datum feature 70 f on the shield. When theshield is in the shield retaining position, the shield retention meansacts to urge the pairs of datum features to abut, thereby constrainingthe position of the shield with respect to the position of the shieldretention stage. Datum features may be datum surfaces, as is shown inthe preferred embodiment of FIG. 6, or they may be datum edges or datumvertices, or combinations of datum surfaces, datum edges, and datumvertices.

Turning now to figures FIG. 7A, FIG. 7B, FIG. 8A, FIG. 8B, FIG. 9, andFIG. 10, shown are various features and embodiments of shield 60according to the present disclosure.

FIG. 7A is a perspective view of a shield showing a first shieldingsurface 61 a, a second shielding surface 61 b, and shield edge 63. Ionsfrom the ion beam irradiating means that are blocked by the shield, and,in particular, the ions that are blocked by first shielding surface 61a, are prevented from milling the sample. Ions not blocked by the shieldmay be used to prepare the sample for observation and analysis. When theion beam is operating, ions may or may not impact second shieldingsurface 61 b. Whether ions do impact second shielding surface 61 bdepends on a number a factors including, but not limited to: the size ofthe ion beam; the angle at which the ion beam is directed; and, theposition at which the ion beam is directed. It is a preferred embodimentof the shield that second shielding surface 61 b be made of the samematerial as first shielding surface 61 a. In preferred embodiments,shield 60 is a generally planar rigid member, having one or moreshielding surfaces that are smooth and may be polished, having a datumsurface and at least an additional datum feature for facilitatingaccurate placement within the shield retention stage. Preferredmaterials for the shield are non-magnetic metals with lowsputtering-yield including, but not limited to, tantalum or titanium.Lower cost embodiments of shield 60 may comprise core material 66 forthe majority of the shield and cladding material 67 used for theshielding surfaces. Preferred core materials include, but are notlimited to, copper. Preferred cladding materials include, but are notlimited to, tantalum or titanium. Figures FIG. 15A and FIG. 15Billustrate two different embodiments of a shield 60, wherein eachembodiment is shown comprising a combination of core material 66 andcladding material 67.

FIG. 7B shows the same shield as shown in FIG. 7A, but from a differentangle thereby illustrating the position and nature of a plurality ofdatum features 70 d and 70 f.

FIG. 8A shows the same shield as shown in FIG. 7A and FIG. 7B. FIG. 8Ashows a perspective view of shield 60 from the side of the shieldclosest to the sample during ion beam sample preparation. Proximalsample surface 62 may be used to adhere the sample material to beprepared in the apparatus. Datum surface 72 is a datum feature that is asurface. In a preferred embodiment, at least a portion of proximalsample surface 62 may be coextensive with at least a portion of datumsurface 72. Shield edge 63 is formed by the intersection of firstshielding surface 61 a and proximal sample surface 62. The angle betweenfirst shielding surface 61 a and proximal sample surface 62 has animpact on the quality of milling performed on the sample by the ionbeam. A preferred embodiment is achieved when said first shieldingsurface 61 a meets said proximal sample surface 62 at an angle of lessthan about 90 degrees and more than about 80 degrees. An even morepreferred embodiment is achieved when said first shielding surface 61 ameets said proximal sample surface 62 at an angle of less than about 87degrees and more than about 83 degrees.

FIG. 8B shows the same shield as shown in FIG. 8A, but from a differentangle thereby illustrating the position and nature of a plurality ofdatum features 70 d and 70 f, and datum surface 72, present on shield60.

FIG. 9 shows a perspective view of shield 60, having first shieldingsurface 61 a, second shielding surface 61 b, shield edge 63, andadditionally comprising a visible alignment mark 65. When the shield isheld in the shield retaining position, the visible alignment mark ispositioned so that it indicates the approximate location where a portionof the ion beam will pass over shield edge 63 and impact the sample whenthe shield edge is substantially perpendicular to the central ion beamaxis.

FIG. 10 shows a perspective view of shield 60 from the side of theshield closest to the sample during ion beam sample preparation.Proximal sample surface 62 may be used to adhere the sample material tothe shield prior to ion beam sample preparation in the apparatus.Recessed portion 64 provides a recessed portion of proximal samplesurface 62 useful for flowing adhesive under the sample, therebyfacilitating the durable adhering of sample to shield. Preferredmaterials used to adhere the sample to the shield include, but are notlimited to: UV cured glue, light cured glue, superglue, silver paint,and wax.

Turning now to FIG. 11A, shown is a perspective view of shield 60,shielding surface 61, sample 8 durably adhered to the shield, andvisible alignment mark 65. FIG. 11A depicts the sample prior to ion beampreparation. FIG. 11B is a perspective view of the same objects depictedin FIG. 11A. However, FIG. 11B represents the sample after ion beamsample preparation. Shielding surface 61 intercepts a portion of the ionbeam, which travels along central ion beam axis 22. A portion of sample8 is sputtered away by the ion beam during sample preparation, therebyexposing a portion of the sample lying in the plane defined by shieldedge 63 and central ion beam axis 22. A sample prepared in this way willbe suitable for observation or analysis with a variety of microscopic orspectroscopic techniques, particularly those requiring a highly polishedplanar surface.

FIGS. 12A and 12B illustrate another embodiment of shield 60, in which asample clamping means 68 is formed integrally with the shield on theproximal sample surface 62. FIG. 12A depicts this shield prior toclamping a sample, while FIG. 12B depicts this shield after sample 8 hasbeen secured to the shield by means of sample clamping means 68. Inanother embodiment, sample clamping means 68 may be formed separately,and then coupled to the shield prior to clamping the sample. Adhesivemay be applied between the sample clamping means and the sample tofurther ensure the sample does not move with respect to the shield.

Use of the apparatus shown in FIG. 1 may proceed with reference to thefollowing steps: outside of the vacuum chamber, a sample may be durablyadhered to a shield; with the chamber cover removed, the sample andshield combination may be set in the shield retaining position of theshield retention stage; the chamber cover may then be replaced; with thechamber cover in place on the vacuum chamber, the vacuum pump means maybe operated to evacuate the vacuum chamber through the pumping manifold,thereby obtaining vacuum levels appropriate for ion beam milling; theion beam irradiating means may then be operated to prepare the sample.When the sample is prepared to the extent desired by the user of theapparatus, the ion beam irradiating means may be turned off, the vacuumchamber may be returned to atmospheric conditions, the chamber cover maybe removed, and the prepared sample may be removed from the apparatusalong with the shield to which it was previously adhered. A microscopemay be fitted with a shield retention stage so that the prepared sampleand shield may be retained, and thereby the prepared region of thesample may be observed in the microscope. After observation the user maydecide that additional sample preparation is needed. Since the sample isstill durably adhered to the shield, it is a simple matter to return thesample and shield to the vacuum chamber for additional processing. Thedatum features on both the shield and the shield retention stage ensurethat the shield may be retained in substantially the same position andorientation each time the sample is processed in the apparatus. A kitcomprising a shield retention stage 40 with a plurality of datumfeatures 70 a, 70 c, and 70 e, shield retention means 42, and at leastone shield 60 with a plurality of datum features 70 b, 70 d, and 70 fmay be supplied for fitting to a microscope. Such a kit facilitates themicroscopic observation of samples prepared in the ion beam samplepreparation apparatus 2.

Turning now to FIG. 13A and FIG. 13B, shown are another embodiment of anion beam sample preparation apparatus according to the presentdisclosure. The embodiment of FIG. 13A and FIG. 13B comprises: a vacuumchamber 10 in which a sample 8 is prepared; chamber cover 18 which sealsvacuum chamber 10 from the outside atmosphere; vacuum pump means 90, andpumping manifold 92 which together bring vacuum chamber 10 to vacuumlevels appropriate for ion beam milling; tilting ion beam irradiatingmeans 36 and tilt drive 38, which direct an ion beam having a centralion beam axis 22 toward sample 8; a shield 60, which shields at least aportion of sample 8 from at least a portion of the ion beam; a rotatingshield retention stage 50, which holds and accurately positions shield60 with respect to the direction and extent of the ion beam; a shieldretention means 42, which both retains shield 60 in rotating shieldretention stage 50 and also urges shield 60 to remain in a positionwhereby the ion beam may prepare sample 8; a rotation drive 52, whichrotates the rotating shield retention stage 50 about rotation axis 54;and vacuum seal 56, which maintains the vacuum in vacuum chamber 10,while allowing rotating shield retention stage 50 to move about rotationaxis 54. In preferred embodiment, rotation axis 54 lies substantially inthe plane defined by the abutment of the proximal sample surface 62 withthe sample 8. Shield 60 of figures FIG. 13A and FIG. 13B has the samefeatures, functions, and aspects possessed by shield 60 shown in figuresFIG. 3A, FIG. 3B, FIG. 5A, FIG. 5B, FIG. 6, FIG. 7A, FIG. 7B, FIG. 8A,and FIG. 8B.

With continuing reference to FIG. 13A and FIG. 13B, the ion beampreferably comprises noble gas ions. Elements used for the ion beam mayinclude but are not limited to: argon, xenon, and krypton. The ion beammay also comprise a mixture of ions and neutrals. Shield retention stage50 is disposed in vacuum chamber 10 in a predetermined position andorientation with respect to central beam axis 22. Rotating shieldretention stage 50 may additionally comprise means for measuring therotation angle of the stage. Rotation drive 52 may additionally comprisemeans to reach and maintain accurate angular position. Rotation drive 52may additionally comprise means to reach and maintain accurate angularspeed. Rotation drive 52 enables rotating shield retention stage 50 torotate about rotation axis 54. In a preferred embodiment, shield edge 63is disposed substantially perpendicular to rotation axis 54 when shield60 is held in the shield retaining position.

In the apparatus of FIG. 13A and FIG. 13B, tilting ion beam irradiatingmeans 36 and tilt drive 38 enable the ion beam to prepare the sample bydirecting central ion beam axis 22 toward sample 8 from more than oneangle. FIG. 13A shows tilting ion beam irradiating means 36 at a firstangle,

while FIG. 13B shows tilting ion beam irradiating means 36 at a secondangle. In a preferred embodiment, tilting ion beam irradiating means 36and tilt drive 38 are adapted to provide a variable degree of tilt anglewhile maintaining central ion beam axis 22 substantially perpendicularto shield edge 63 for at least a portion of tilt angle. In a preferredembodiment, tilting ion beam irradiating means 36 and tilt drive 38 areadapted to provide a variable degree of tilt angle while central ionbeam axis 22 substantially intersects rotation axis 54 for at least aportion of tilt angle.

Features and aspects of rotating shield retention stage 50 may be betterunderstood now with reference to FIG. 14A and FIG. 14B and the writtendescription that follows.

FIG. 14A shows a perspective schematic view of rotating shield retentionstage 50, on which sample 8 has been durably adhered to shield 60 priorto placing the shield and sample combination in a shield retainingposition of rotating shield retention stage 50. Shield 60 has ashielding surface 61, which is positioned in relation to sample 8 toshield at least a portion of said sample 8 from at least a portion ofthe ion beam. Rotation drive 52 enables rotating shield retention stage50 to rotate about rotation axis 54. In a preferred embodiment, shieldedge 63 is disposed to be substantially perpendicular to rotation axis54 when shield 60 is held in the shield retaining position. Also shownin FIG. 14A is a section line indicating the section view shown in FIG.14B.

FIG. 14B shows a section view illustrating the position and function ofthe shield retention means, which is part of rotating shield retentionstage 50. In FIG. 14B shield retention means first member 42 a urgesshield retention means second member 42 b against shield 60. The actionof shield retention means first member 42 a also urges shield 60 againstrotating shield retention stage 50 and thereby maintains the position ofshield 60 within rotating shield retention stage 50 while the sample isprepared by the ion beam. An embodiment of the shield retention meansmay comprise a spring for shield retention means first member 42 a and asolid member as shield retention means second member 42 b configured toslide within a cavity in rotating shield retention stage 50. The shieldretention means also has a shield releasing position in which the shieldand sample are not held in the rotating shield retention stage 50. Theshield releasing position may be identical to the shield releasingposition 48 illustrated in FIG. 4. In a preferred embodiment, rotationaxis 54 lies substantially in the plane defined by the abutment of theproximal sample surface 62 with the sample 8.

The rotating shield retention stage 50 has the same plurality of datumfeatures as shown on the non-rotating shield retention stage of FIG. 6.In addition, the rotating shield retention stage 50 datum features allowthe interchangeable use of shield 60 previously described. The datumfeatures of the shield retention stage 40 and the rotating shieldretention stage 50 are substantially identical in design, and therebyfacilitate the easy interchange of shields between the stages. By meansof the two positions provided by the shield retention means, namelyshield retaining position 46, as shown in FIG. 3B, and shield releasingposition 48, as shown in FIG. 4, a shield may be removably andreplaceably secured in rotating shield retention stage 50. A sample thathas been durably adhered to shield 60 may be processed, removed, andthen reprocessed by simply placing it in the shield retaining positionand preparing the sample again in the ion beam. The datum features onboth shield and shield retention stage assure that the shield may bepositioned in a substantially identical position and orientationmultiple times. In preferred embodiments that include rotating shieldretention stage 50, central ion beam axis 22 passes substantiallythrough rotation axis 54 in the region above shield edge 63. After thesample has been prepared by the ion beam in the vacuum chamber, chambercover 18 may be removed, and then the shield and sample may be removedfor observation in a microscope.

Use of the apparatus of figures FIG. 13A and FIG. 13B may proceedaccording to all of the steps disclosed for the use of the apparatus ofFIG. 1 and FIG. 2. However, the rotating shield retention stage FIG. 13Aand FIG. 13B gives the user additional capabilities. In particular, theuse of the rotating shield retention stage during sample preparation mayimprove the evenness of the prepared region if that region of the samplehas local variations in physical consistency that lead to differentrates of preparation by the ion beam. Rotation during sample preparationmay have a beneficial leveling effect on such a sample. In addition, theuser may rotate the rotating shield retention stage about the rotationaxis to a desired angle before sample preparation, during samplepreparation, or after sample preparation. Also, the rotation drive andthe tilt drive may operate in concert to accurately and repeatablycontrol the ion beam tilt as a function of the rotation angle of therotating shield retention stage. Thus, the user has increasedflexibility in exposing and preparing a region of interest in the samplefor later microscopic observation.

With continuing reference to FIG. 13A and FIG. 13B, the ion beampreferably comprises noble gas ions. Elements used for the ion beam mayinclude but are not limited to: argon, xenon, and krypton. The ion beammay also comprise a mixture of ions and neutrals. Rotating shieldretention stage 50 is disposed in vacuum chamber 10 in a predeterminedposition and orientation with respect to central ion beam axis 22.Rotating shield retention stage 50 may additionally comprise means formeasuring the rotation angle of the stage. Rotation drive 52 mayadditionally comprise means to reach and maintain accurate angularposition. Rotation drive 52 may additionally comprise means to reach andmaintain accurate angular speed. In addition, shield 60 of FIG. 13A andFIG. 13B has the same features, functions, and aspects possessed byshield 60 shown in figures FIG. 3A, FIG. 3B, FIG. 5A, FIG. 5B, FIG. 6,FIG. 7A, FIG. 7B, FIG. 8A, FIG. 8B, FIG. 14A, and FIG. 14B. In apreferred embodiment, as shown in FIG. 14A and FIG. 14B, rotation axis54 lies substantially in the plane defined by the abutment of theproximal sample surface 62 with the sample 8.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. For example, it may be desirable to combine features shown invarious embodiments into a single embodiment. For example, materials oralloys that are both non-magnetic and have low sputtering-yield may beused with success for shielding surfaces and may be constructed and usedentirely within the spirit and scope of the present disclosure.Therefore, the spirit and scope of the appended claims should not belimited to the description of the preferred versions contained herein.

Any element in a claim that does not explicitly state “means for”performing a specified function, or “step for” performing a specificfunction, is not to be interpreted as a “means” or “step” clause asspecified in 35 U.S.C. Section 112, Paragraph 6. In particular, the useof “step of” in the claims herein is not intended to invoke theprovisions of 35 U.S.C. Section 112, Paragraph 6.

The invention claimed is:
 1. A method of operating an ion beam samplepreparation apparatus having a tilting ion beam irradiating means toprepare a sample, the sample durably adhered to a shield, the methodcomprising the steps of: a) receiving the shield into a shield retentionstage, the shield retention stage being further characterized as havinga first datum feature and a second datum feature, the shield beingfurther characterized as having a third datum feature and a fourth datumfeature; b) retaining said shield in the shield retention stage with ashield retention means such that: i) the first datum feature of theshield retention stage abuts the third datum feature of the shield, and,ii) the second datum feature of the shield retention stage abuts thefourth datum feature of the shield; iii) a first shielding surface ofthe shield is disposed in the path of the ion beam and positioned toshield a portion of the ion beam directed at the first shielding surfacewhen said shield is held in the shield retention stage; c) operating atilt drive such that the tilting ion beam irradiating means is disposedat a first tilt angle with respect to the shield; and, d) operating thetilting ion beam irradiating means at the first tilt angle to project anion beam toward the first shielding surface.
 2. The method of claim 1further comprising the steps of: a) operating the tilt drive such thatthe tilting ion beam irradiating means is disposed at a second tiltangle with respect to the shield; and, b) operating the tilting ion beamirradiating means at the second tilt angle to project an ion beam towardthe first shielding surface.
 3. A method of operating an ion beam samplepreparation apparatus having a tilting ion beam irradiating means toprepare a sample, the sample durably adhered to a shield, the methodcomprising the steps of: a) receiving the shield into a rotating shieldretention stage, the rotating shield retention stage being furthercharacterized as having a first datum feature, a second datum feature, arotation axis located substantially in the plane of the first datumfeature, and a rotation drive for rotating the rotating shield retentionstage around the rotation axis, the shield being further characterizedas having a third datum feature and a fourth datum feature; b) retainingsaid shield in the rotating shield retention stage with a shieldretention means such that: i) the first datum feature of the rotatingshield retention stage abuts the third datum feature of the shield, and,ii) the second datum feature of the rotating shield retention stageabuts the fourth datum feature of the shield; iii) a first shieldingsurface of the shield is disposed in the path of the ion beam andpositioned to shield a portion of the ion beam directed at the firstshielding surface when said shield is held in the rotating shieldretention stage; c) operating a tilt drive such that the tilting ionbeam irradiating means is disposed at a first tilt angle with respect tothe shield; and, d) operating the tilting ion beam irradiating means atthe first tilt angle to project an ion beam toward the first shieldingsurface; e) operating the rotation drive such that the rotating shieldretention stage rotates at least a portion of one rotation while the ionbeam prepares the sample.
 4. The method of claim 3 further comprisingthe steps of: a) operating the tilt drive such that the tilting ion beamirradiating means is disposed at a second tilt angle with respect to theshield; and, b) operating the tilting ion beam irradiating means at thesecond tilt angle to project an ion beam toward the first shieldingsurface.